let then_blk = self.lower_block(then, false);
let then_expr = self.expr_block(then_blk, ThinVec::new());
let (then_pats, scrutinee, desugar) = match cond.node {
- // `<pat> => <then>`
+ // `<pat> => <then>`:
ExprKind::Let(ref pats, ref scrutinee) => {
let scrutinee = self.lower_expr(scrutinee);
let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
let desugar = hir::MatchSource::IfLetDesugar { contains_else_clause };
(pats, scrutinee, desugar)
}
- // `true => then`:
+ // `true => <then>`:
_ => {
// Lower condition:
let cond = self.lower_expr(cond);
- // Wrap in a construct equivalent to `{ let _t = $cond; _t }`
- // to preserve drop semantics since `if cond { ... }`
- // don't let temporaries live outside of `cond`.
let span_block = self.mark_span_with_reason(CondTemporary, cond.span, None);
// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
// to preserve drop semantics since `if cond { ... }` does not
hir::ExprKind::Match(P(scrutinee), vec![then_arm, else_arm].into(), desugar)
}
// FIXME(#53667): handle lowering of && and parens.
- ExprKind::While(ref cond, ref body, opt_label) => {
- // Desugar `ExprWhileLet`
- // from: `[opt_ident]: while let <pat> = <sub_expr> <body>`
- if let ExprKind::Let(ref pats, ref sub_expr) = cond.node {
- // to:
- //
- // [opt_ident]: loop {
- // match <sub_expr> {
- // <pat> => <body>,
- // _ => break
- // }
- // }
-
- // Note that the block AND the condition are evaluated in the loop scope.
- // This is done to allow `break` from inside the condition of the loop.
- let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| {
- (
- this.lower_block(body, false),
- this.expr_break(e.span, ThinVec::new()),
- this.with_loop_condition_scope(|this| P(this.lower_expr(sub_expr))),
- )
- });
+ ExprKind::While(ref cond, ref body, opt_label) => self.with_loop_scope(e.id, |this| {
+ // Note that the block AND the condition are evaluated in the loop scope.
+ // This is done to allow `break` from inside the condition of the loop.
- // `<pat> => <body>`
- let pat_arm = {
- let body_expr = P(self.expr_block(body, ThinVec::new()));
- let pats = pats.iter().map(|pat| self.lower_pat(pat)).collect();
- self.arm(pats, body_expr)
- };
-
- // `_ => break`
- let break_arm = {
- let pat_under = self.pat_wild(e.span);
- self.arm(hir_vec![pat_under], break_expr)
- };
-
- // `match <sub_expr> { ... }`
- let match_expr = self.expr_match(
- sub_expr.span,
- sub_expr,
- hir_vec![pat_arm, break_arm],
- hir::MatchSource::WhileLetDesugar,
- );
+ // `_ => break`:
+ let else_arm = {
+ let else_pat = this.pat_wild(e.span);
+ let else_expr = this.expr_break(e.span, ThinVec::new());
+ this.arm(hir_vec![else_pat], else_expr)
+ };
- // `[opt_ident]: loop { ... }`
- let loop_block = P(self.block_expr(P(match_expr)));
- let loop_expr = hir::ExprKind::Loop(
- loop_block,
- self.lower_label(opt_label),
- hir::LoopSource::WhileLet,
- );
- // Add attributes to the outer returned expr node.
- loop_expr
- } else {
- self.with_loop_scope(e.id, |this| {
+ // Handle then + scrutinee:
+ let then_blk = this.lower_block(body, false);
+ let then_expr = this.expr_block(then_blk, ThinVec::new());
+ let (then_pats, scrutinee, desugar, source) = match cond.node {
+ ExprKind::Let(ref pats, ref scrutinee) => {
+ // to:
+ //
+ // [opt_ident]: loop {
+ // match <sub_expr> {
+ // <pat> => <body>,
+ // _ => break
+ // }
+ // }
+ let scrutinee = this.with_loop_condition_scope(|t| t.lower_expr(scrutinee));
+ let pats = pats.iter().map(|pat| this.lower_pat(pat)).collect();
+ let desugar = hir::MatchSource::WhileLetDesugar;
+ (pats, scrutinee, desugar, hir::LoopSource::WhileLet)
+ }
+ _ => {
// We desugar: `'label: while $cond $body` into:
//
// ```
// }
// ```
- // `true => then`:
- let then_pat = this.pat_bool(e.span, true);
- let then_blk = this.lower_block(body, false);
- let then_expr = this.expr_block(then_blk, ThinVec::new());
- let then_arm = this.arm(hir_vec![then_pat], P(then_expr));
-
- // `_ => break`:
- let else_pat = this.pat_wild(e.span);
- let else_expr = this.expr_break(e.span, ThinVec::new());
- let else_arm = this.arm(hir_vec![else_pat], else_expr);
-
// Lower condition:
- let span_block = this.mark_span_with_reason(CondTemporary, cond.span, None);
let cond = this.with_loop_condition_scope(|this| this.lower_expr(cond));
+ let span_block = this.mark_span_with_reason(CondTemporary, cond.span, None);
// Wrap in a construct equivalent to `{ let _t = $cond; _t }`
- // to preserve drop semantics since `if cond { ... }` does not
+ // to preserve drop semantics since `while cond { ... }` does not
// let temporaries live outside of `cond`.
let cond = this.expr_drop_temps(span_block, P(cond), ThinVec::new());
- let match_expr = this.expr_match(
- cond.span,
- P(cond),
- vec![then_arm, else_arm].into(),
- hir::MatchSource::WhileDesugar,
- );
+ let desugar = hir::MatchSource::WhileDesugar;
+ // `true => <then>`:
+ let pats = hir_vec![this.pat_bool(e.span, true)];
+ (pats, cond, desugar, hir::LoopSource::While)
+ }
+ };
+ let then_arm = this.arm(then_pats, P(then_expr));
- hir::ExprKind::Loop(
- P(this.block_expr(P(match_expr))),
- this.lower_label(opt_label),
- hir::LoopSource::While,
- )
- })
- }
- }
+ // `match <scrutinee> { ... }`
+ let match_expr = this.expr_match(
+ scrutinee.span,
+ P(scrutinee),
+ hir_vec![then_arm, else_arm],
+ desugar,
+ );
+
+ // `[opt_ident]: loop { ... }`
+ hir::ExprKind::Loop(
+ P(this.block_expr(P(match_expr))),
+ this.lower_label(opt_label),
+ source
+ )
+ }),
ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
hir::ExprKind::Loop(
this.lower_block(body, false),
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